Method for controlling the material flow during the deep-drawings of sheet metal, and deep-drawing tool

ABSTRACT

A method for controlling the material flow during the deep-drawing of sheet metal involves compressing the edges of the sheet metal ( 1 ) between at least one upper stopper ( 13 ) and at least one lower stopper ( 6, 7 ) during the deep-drawing process, with a controllable elastic force ( 8, 9 ). A corresponding deep-drawing tool is also provided. A Z-shaped blocking step ( 11 ) is stamped into the edge ( 1   a ) of the sheet metal when the upper and lower stoppers ( 13, 6, 7 ) are closed, the basic shape is then produced by deep-drawing, maintaining the blocking step ( 11 ) and completely blocking the sheet metal between the stoppers. The sheet metal ( 1 ) is outwardly stretched, and the blocking step ( 11 ) is then reduced in terms of height, facilitating the outward displacement of the sheet metal towards the outside. The deep-drawing tool has a lower stopper including an inner stopper ( 6 ) and an outer stopper ( 7 ). The stoppers are arranged in an annular manner on the edge of the sheet metal ( 1 ) and can be displaced in relation to each other in the holding direction.

FIELD OF THE INVENTION

The invention relates to a method for controlling the material flowduring the deep-drawing of sheet metal, preferably made of high-strengthsteels and/or multiplephase steels or of aluminum as well as to adeep-drawing tool.

BACKGROUND OF THE INVENTION

The use of high-strength steels in car body construction attains evergreater importance within the scope of developing ever lighter motorvehicles. For example, sheet metal plates made of multiple-phase steelsare proposed for planking parts. For planking parts made of deep-drawingmaterials with high hardening values, in particular, it is importantthat the sheet metal plate is stretched-out over an as “large-surface”as possible. For this purpose, it is state of the art to impede thesheet metal plate trailing from outside by means of a blocking step orblocking bead located on the sheet metal stopper. A disadvantageaccording to this method might be involved, if the sheet metalimpediment remains constant throughout the deep-drawing process,particularly if the sheet metal is stretched-out beyond the 20% criticalexpansion in considerably deformed areas and towards the end of thedeep-drawing process. In an article published by S. Beck under theheading “Steuerung des Ziehprozesses durch aktive Ziehsicken”(Controlling the Deep-Drawing Process by Active Drawing Beads) in thebook “Neuere Entwicklungen in der Blechumformung” (Latest Developmentsin Sheet Metal Forming), editor Klaus Siegert, May 2000, the use ofheight-adjustable deep-drawing rods is described, which are used inorder to control strains and stresses occurring in metal forming andthus to control the flow of material. Constructive solutions solelyrelate to a relatively expensive adjustment in height of deep-drawingrods.

Moreover, known from EP 806 256 B1 is a method for controlling thematerial flow during deep-drawing of work pieces like sheet metalforming blanks, wherein the frictional force between work piece andholding-down device is measured through a frictional force sensor toserve as controlling variable for a holding-down force. Also appliedtherein is a segmented holding-down device in order to control theholding-down force of individual holding-down device segments spread atits periphery. This solution, too, is relatively complicated.

SUMMARY OF THE INVENTION

Now, therefore, it is the object of the present invention to provide ageneric method for controlling during deep-drawing of sheet metal platesand an appropriate deep-drawing tool, in which the height adjustmentthrough deep-drawing rods and the expensive frictional force sensors canbe dispensed with.

According to the invention, a method is provided for controlling thematerial flow during the deep-drawing of sheet metal plates, preferablymade of high-strength steels and/or multiple-phase steels or aluminum.The method includes forming the sheet metal plate in a press between adie stamp arranged at a base plate and a matrix arranged at a top plate.The die stamp and the matrix have adapted profiled sections for theformation of die beads at the edges of the sheet metal plate. The edgesof the sheet metal plate are compressed between at least one upper sheetmetal stopper and at least one lower sheet metal stopper during thedeep-drawing process, applying a controllable spring load. The method ofthe invention further includes:

-   a) initially, as the upper and lower sheet metal stoppers are    closed, stamping a Z-shaped blocking step into the sheet metal plate    edge;-   b) then, by maintaining the blocking step and a complete blocking    between the sheet metal stoppers, the drawing of the base form is    completed, with the sheet metal plate being stretched-out from    inside to outside, and-   c) finally, the blocking step is reduced in its height, thus    facilitating the sheet metal trailing from outside.

According to another aspect of the invention, a method for controllingthe material flow during the deep-drawing of sheet metal plates,preferably made of high-strength steels and/or multiple-phase steels oraluminum is provided. The sheet metal plate is formed in a press betweena die stamp arranged at a base plate and a matrix arranged at a topplate. The die stamp and the matrix have adapted profiled sections forthe formation of die beads at the edges of the sheet metal plate. Theedges of said sheet metal plate are compressed between at least oneupper sheet metal stopper and at least one lower sheet metal stopperduring the deep-drawing process by applying a controllable spring load.The method further includes initially, mainly without any bead effect,drawing the base form, while the upper and lower sheet metal stoppersrest upon each other mainly evenly, and then stamping a blocking stepinto the sheet metal plate edge in order to impede the sheet metaltrailing from outside to inside.

According to still another aspect of the invention, a deep-drawing toolis provided for the deep-drawing of sheet metal plates, preferably forexecuting the method discussed above. A die stamp is arranged in a pressat a base plate and a matrix is arranged oppositely at a top plate.Profiled sections are arranged at the die stamp and at the matrix forthe formation of die beads at the edges of the sheet metal plate to bedeformed. At least one upper sheet metal stopper and at least one lowersheet metal stopper are provided. The lower sheet metal stopper includesan inner sheet metal stopper and an outer sheet metal stopper. Thesestoppers are annularly arranged at the edge of the sheet metal plate andare movable relative to each other in the direction of holding.

Pursuant to the inventive method, a Z-shaped blocking step (see feature(a)) is stamped into the sheet metal plate edge at first, i.e. prior tothe actual deep-drawing process as the upper and lower sheet metal platestoppers are closed, wherein the blocking step is then maintained duringcompletion of the base form drawing, thus creating a complete blockingstep by the compressed sheet metal plate stoppers and stretching-out thesheet metal plate from inside towards the outside (see feature (b)).Finally, during the further deep-drawing process, the blocking step isreduced in its height, thus facilitating the sheet metal plate trailingfrom outside (see feature (c)). By way of the inventive 2-shapedblocking step, the sheet metal plate impediment from outside can beincreased on the whole and, by the end of the deep-drawing process, itis possible to reduce and even entirely abandon the sheet metal plateimpediment by reducing the height of the blocking step throughmechanical off-controlling of the deep-drawing step, so that the sheetmetal plate trailing takes place exclusively from outside to inside.

The method being the subject of the present invention may also beapplied by reversing the step for the reverse case by performing thedeep-drawing process without a blocking step at the beginning, asdescribed according to the other method aspect. This provides thestamping of a blocking step by the aid of the sheet metal holding-downdevices only during the deep-drawing process. Hence, the sheet metalplate trailing is impeded by the aid of the blocking step only by theend. This may be of some advantage both for deep-drawing processes withlocally substantial deformation, with it being necessary to “serve1”material, and for sheet metal materials having little breakingelongation, e.g. like aluminum.

The constructive solution provides for a deep-drawing tool as mentionedabove. At least one sheet metal stopper, preferably the lower sheetmetal stopper along the blocking step is divided into an inner and anouter ring and wherein at least one of these rings is movable relativeto the other ring in the direction of holding. The two sheet metalstoppers arranged next to each other may create an adjustable blockingstep for the edge of the sheet metal plate and be pressed against acorresponding firm step of the counter-stopper in order to attain thedesired sheet metal plate impediment. By actuating the outer ring in aholding direction relative to the inner ring, the step can be reducedfrom its initial height with maximal blocking effect down to any desireddrawing depth, and even down to zero in extreme cases. In conformitywith the method according to the other method aspect, this process mayalso be reversed by initially working virtually without any blockingstep between the inner and outer sheet metal stopper and thenswitching-on the effect of the blocking step by increasing the stepbetween the two rings and raising it up to maximal effect till the end.

By way of the inventive bipartite sheet metal stopper and through therelative movement of the outer ring towards the inner ring, adeep-drawing tool with a controllable blocking step is attained. Incontrast with mono-acting tools, the matrix and the upper sheet metalstopper are also movable relative to each other. This deep-drawing toolcan virtually be applied in all conventional presses with controlled ordelayed-trailing die pads.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich a preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view through the inventive deep-drawing toolbetween top plate 2 and base plate 3 of a press;

FIG. 2 is an enhanced view of the central area in FIG. 1; and

FIG. 3 is a sectional view corresponding to the view as per FIG. 1showing the controllable blocking step in five different phases.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings in particular, FIG. 1 shows the sheet metalplate 1 prior to the deep-drawing process with the sheet metal plateedge 1 a as a dashed line with blocking step 11. After the deep-drawingprocess, the sheet metal plate edge 1 b is drawn with a continuous line.Sheet metal plate 1 is located between the deep-drawing stamp 4 andmatrix 5 that are arranged between top plate 2 and base plate 3 of aconventional press. In a conventional manner, base plate 3 is fixed instationary arrangement, while top plate 2 is vertically movable for thedeep-drawing process. At its underside, the upper sheet metal stopper13, which is movable relative to a die plate or matrix 5 possesses astep 16 that corresponds to the blocking step 11 of the sheet metal edge1 a. During the deep-drawing process, the upper sheet metal stopper 13is loaded by spring load 9, also designated as top pneumatic force, andpressed against the sheet metal edge. The two lower sheet metal stoppers6 and 7, which in their upper position 6 a, 7 a, prior to thedeep-drawing process, are represented with a dashed bordering, act ascounter-stoppers. At the lower position 6 b, 7 b these two sheet metalstoppers are shown in hatched lines. The inner sheet metal stopper 6 ispressed by spring load (or lower pneumatic force) 8 and the outer sheetmetal stopper 7 by the stroke dependent counterforce 10 from the bottomagainst the edge of sheet metal plate 1. To shape a forming step, stamp4 possesses a bead 12, while matrix 5 has a corresponding nose 14, whichis shown on FIG. 2, particularly in the upper (dashed line) and lowerposition.

Shown on FIG. 3, in particular, are five different phases for theposition of the two lower, inner and outer sheet metal stoppers 6 and 7:

Phase 1: Close sheet metal stopper

Via the upper sheet metal stopper 13 charged with top force 9 and viathe lower sheet metal stoppers 6,7 acting with bottom force 8, ablocking step 11 is stamped with maximal step height 11.1 into the sheetmetal plate edge 1 a. The outer sheet metal stopper 7 a rests with itsunderside on the support surface 15 of the inner sheet metal stopper 6a.

Phase 2: Stretching the base form

By completely blocking and maintaining the maximal step height 11.2, thebase form is drawn completely, with the sheet metal plate beingstretched-out exclusively from inside to outside. This direction ofmaterial flow is indicated by arrows PI.

Phase 3: Start forming the forming step on the stamp

By causing the stroke-dependent counterforce 10 to act upon the outerlower sheet metal stopper 7, the blocking step is reduced in its stepheight 11.3, thus facilitating the sheet metal trailing from outside.(vide arrow P2).

Phase 4: Further deforming the forming step

By way of further reducing the blocking step height 11.4, the requiredsheet metal trailing is caused to intensively take place from outside.

Phase 5: Complete forming

There being no step height 11.5 any longer and because of the virtuallydropped blocking step, the sheet metal trailing takes place exclusivelyfrom outside (vide arrow P3).

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

1. A method for controlling the material flow during the deep-drawing ofsheet metal plates, the method comprising: forming the sheet metal platein a press between a die stamp arranged at a base plate and a matrixarranged at a top plate; providing the die stamp and the matrix withadapted profiled sections for the formation of die beads at the edges ofsaid sheet metal plate compressing the edges of said sheet metal platebetween at least one upper sheet metal stopper and at least one lowersheet metal stopper during the deep-drawing process, applying acontrollable spring load; initially, as the upper and lower sheet metalstoppers are closed, stamping a Z-shaped blocking step into the sheetmetal plate edge; then, by maintaining the blocking step and a completeblocking between said sheet metal stoppers, completing the drawing ofthe base form with said sheet metal plate being stretched-out frominside to outside; and finally, reducing the blocking step in itsheight, thus facilitating the sheet metal trailing from outside.
 2. Amethod pursuant to claim 1, wherein by the end, through completeabandonment of the blocking step, the sheet metal trailing takes placeexclusively from outside to inside.
 3. A method for controlling thematerial flow during the deep-drawing of sheet metal plates, made ofhigh-strength steels and/or multiple-phase steels or aluminum, themethod comprising: forming the sheet metal plate in a press between adie stamp arranged at a base plate and a matrix arranged at a top plate,the die stamp and the matrix having adapted profiled sections for theformation of die beads at the edges of said sheet metal plate; andcompressing the edges of said sheet metal plate between at least oneupper sheet metal stopper and at least one lower sheet metal stopperduring the deep-drawing process, applying a controllable elastic load;initially, mainly without any bead effect, drawing the base form, whilethe upper and lower sheet metal stoppers rest upon each other mainlyevenly; and then stamping a blocking step into the sheet metal plateedge in order to impede the sheet metal trailing from outside to inside.4. A deep-drawing tool for the deep-drawing of sheet metal plates, forexecuting a method including stamping a blocking step into the sheetmetal plate edge, said tool comprising: a die stamp arranged in a pressat a base plate and a matrix arranged oppositely at a top plate;profiled sections arranged at the die stamp and at the matrix for theformation of die beads at the edges of the sheet metal plate to bedeformed; and at least one upper sheet metal stopper and at least onelower sheet metal stopper the lower sheet metal stopper including aninner sheet metal stopper and an outer sheet metal stopper, saidstoppers being annularly arranged at the edge of said sheet metal plateand being movable relative to each other in the direction of holding. 5.A deep-drawing tool pursuant to claim 4, wherein the lower inner sheetmetal stopper has a support surface onto which the outer sheet metalstopper comes to rest in the lower relative position as compared withthe inner sheet metal stopper.
 6. A deep-drawing tool pursuant to claim4, wherein the two lower sheet metal stoppers with their upper sidescreate the blocking step for the edge of said sheet metal plate that isadjustable.
 7. A deep-drawing tool pursuant to claim 1, wherein a stepcorresponding to the maximal step height of said blocking step isarranged at the underside of the upper sheet metal stopper.